TH 

9057 

M3 
1894 


IC-NRLF 


31S    372 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 
WEATHER    BUREAU., 


CIRCULAR  OF  INFORMATION. 


PROTECTION   FROM    LIGHTNING 


BY 


ALEXANDEK  ^ 

U.  S.   WEATHER  Bl/REAU. 


3d  Edition. 


Published  by  authority  of  the  Secretary  of  Agriculture. 


f7D.  0. 

WEATHER   BUKEAU. 
1894. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 
5.  WEATHER    BUREAU. 


CIRQULAR  OF  INFORMATION. 


PROTECTION   FROM    LIGHTNING 


BY 


ALEXAKDEK 

U.  8.  WEATHER  BUREAU 


3d  Edition. 


Published  by  authority  of  the  Secretary  of  Agriculture. 


WASHINGTON,  D.  C.: 

WEATHER   BUREAU. 
1894. 


LETTER    OF   TRANSMITTAL. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

WEATHER  BUREAU, 
Washington,  D.  C.,  May  14,  1894. 

SIR:  I  have  the  honor  to  transmit  herewith   the  accompanying 
circular  of  information  entitled  "  Protection  from  Lightning  "  and  to 
recommend  its  publication  as  a  Circular  of  the  Weather  Bureau. 
Very  respectfully, 

MARK  W.  HARRINGTON, 

Chief  of  Weather  Bureau. 
Hon.  J.  STERLING  MORTON, 

Secretary  of  Agriculture. 


032 


LETTER    OF    SUBMTTTAL. 


WASHINGTON,  D.  C.,  April  24,  1894. 

SIR  :  In  accordance  with  the  direction  of-  the  Honorable  the  Secre- 
tary of  Agriculture,  in  letter  of  April  18,  1894,  the  accompanying 
paper,  entitled  "  Protection  from  Lightning,"  is  submitted  for  publi- 
cation as  a  circular  of  information.  Upon  few  subjects  is  the  com- 
munity so  liable  to  be  misled  as  the  question  of  the  best  methods  of 
protecting  life  and  property  from  lightning.  The  following  pages 
give  statistics  of  actual  losses,  the  theory  of  protection  in  language 
free  from  technicalities,  a  collection  of  practical  rules  for  guidance  in 
selecting  and  maintaining  conductors,  and,  finally,  a  notable  illustra- 
tion of  the  successful  use  of  protectors. 

The  aim  of  the  paper  is  to  furnish  information  of  practical  value 
to  all  classes,  and  especially  to  farmers,  builders,  and  physicians. 
Very  respectfully, 

ALEXANDER  McAoiE. 
MARK  W.  HARRINGTON, 

Chief  of  Weather  Bureau. 

6 


PROTECTION  FROM  LIGHTNING. 


At  the  Aberdeen  meeting  of  the  British  Association  for  the  Ad- 
vancement of  Science  Sir  William  Thomson  made  the  remark,  "  If 
I  urge  Glasgow  manufacturers  to  put  up  lightning  rods  they  say  it  is 
cheaper  to  insure  than  to  do  so." 

This  was  the  answer  given  by  practical  business  men,  concerned 
only  with  questions  of  profit  and  loss,  to  the  foremost  physicist  of 
our  time;  and  their  answer  will  serve  as  fairly  representing  views 
widely  held,  founded  upon  the  double  belief  that  the  risk  from  light- 
ning is  not  so  very  great  and  the  protection  afforded  by  the  present 
methods  not  sufficiently  certain  to  warrant  implicit  confidence  and 
justify  the  necessary  expense. 

The  recent  remarkable  experiments  of  Dr.  Oliver  Lodge,  in  his 
lectures  before  the  Society  of  Arts,  opposing  and  to  some  degree  di- 
rectly contradicting  the  empirical  rules  of  the  Lightning  Rod  Con- 
ference, have  given  support  to  the  belief  that  the  protection  was 
uncertain.  Indeed,  realizing  that  his  work  might  be  misinterpreted, 
Lodge  has  stated  "  an  idea  at  one  time  got  abroad  that  my  experiments 
proved  existing  lightning  conductors  to  be  useless  or  dangerous ;  this 
is  an  entire  misrepresentation.  Almost  any  conductor  is  probably 
better  than  none,  but  few  or  no  conductors  are  absolute  and  complete 
safeguards.  Certain  habits  of  lightning  rod  practice  may  be  improved 
and  the  curious  freaks  or  vagaries  of  lightning  strokes  in  protected 
buildings  are  intelligible  without  any  blame  attaching  to  the  con- 
ductor; but  this  is  very  different  from  the  contention  that  lightning, 
rods  are  unnecessary  and  useless.  They  are  essential  to  anything  like 
security."1 

What  Lodge's  brilliant  experimental  work  does  show  is  that  the 
momentum  of  an  electric  current  can  not  be  overlooked  in  a  light- 
ning discharge.  The  old  "  drain-pipe  "  idea  of  conveying  electricity 
gently  from  cloud  to  earth  must  give  place  to  the  new  proposition, 
based  upon  recent  discoveries,  that  even  draining  off  must  be  done  in 
an  appropriate  way  to  be  effective.  To  illustrate,  the  rocks  and  trees 
upon  a  mountain  side  may  influence  and  determine  the  course  of  a 
mountain  stream,  but  even  a  good  sized  channel  would  not  suffice  to 
carry  off  safely  an  avalanche,  or  control  the  path  of  a  landslide ;  so 
with  lightning.  In  the  past  four  years  we  have  learned,  through  the 
work  of  Hertz  and  others,  that  when  an  electric  current  flows  steadily 
1  Page  VI.  "  Lightning  Conductors  and  Lightning  Guards." 


8 

in  one  direction  in  a  cylindrical  wire  its  intensity  is  the  same  in  all 
parts  of  the  wire ;  but  if  the  current  be  of  an  oscillatory  character, 
i.  e.,  a  current  which  rapidly  reverses  its  direction,  the  condition  no 
longer  holds,  and  if  the  alternations  are  very  rapid  the  interior  of  the 
wire  may  be  almost  free  from  current.  If  lightning  then  be  a  dis- 
charge of  an  oscillatory  character,  it  may  happen  that  the  current 
down  the  lightning  rod  would  be  only  skin  deep.  The  experiments  of 
Tesla  and  Elihu  Thomson  with  currents  of  great  frequency  of  alter- 
nation and  very  high  potentials  open  the  door  to  systematic  study  of 
discharges  such  as  the  ordinary  lightning  flash.  In  daily  work  cur- 
rents of  this  type  are  coming  more  and  more  into  prominence,  and 
the  time  is  not  far  distant  when  the  lightning  flash  will  be  studied  as 
an  electrical  discharge  of  this  character.  Protection  entirely  adequate 
for  such  discharges  will  then  be  forthcoming.  Indeed,  the  reasons 
why  present  methods  occasionally  fail  are  now  understood,  and  the 
proper  remedies  apparent. 

And  first  let  us  see  whether  it  is  cheaper  to  insure  than  to  provide 
proper  protection.  Foreign  countries,  especially  Germany,  France, 
and  Great  Britain,  have  recognized  the  importance  of  obtaining 
reliable  data  concerning  the  loss  of  life  and  damage  to  property 
through  lightning.  Perhaps  the  work  of  the  Royal  Prussian  Bureau 
of  Statistics1  gives  the  fullest  and  most  detailed  accounts  of  the 
damage  done  by  lightning  in  Germany,  and  the  relative  injury. 
Statistics  are  available  for  the  number  of  houses  struck,  the  number 
of  fires,  the  character  of  the  roofing,  soil,  etc. 

In  1891  the  Weather  Bureau  issued  to  its  observers  instructions  to 
report  at  the  end  of  every  month  the  names,  with  corroborative  dates 
and  places,  of  all  persons  killed  by  violent  windstorms,  tornadoes, 
and  lightning.  During  1890  somewhat  similar  statistics  had  been 
gathered,  but  the  returns  were  less  systematically  arranged.  In  pre- 
paring the  Weather  Bureau  lists,  observers  were  directed  to  examine 
all  daily  papers  published  in  their  respective  cities,  consult  all  local 
authorities,  and  make  inquiry  if  necessary.  Naturally,  where  de- 
pendence was  had  upon  newspaper  items,  there  resulted  much  dupli- 
cation, but  in  verifying  names  and  dates  the  duplicates  quickly 
appear  and  exaggerated  reports  are  easily  confined  to  proper  limits. 

From  the  Weather  Bureau  records  which  have  been  tabulated,  it 
appears  that  in  the  United  States,  for  the  four  years  1890-'93,  784  lives 
were  lost,  an  average  of  196  lives  per  year. 

It  is  also  evident  that  these  lives  were  practically  all  lost  in  five 
months — April  to  September — and  that  in  June  and  July  the  maxi- 
mum death  rate  occurs. 

The  Weather  Bureau  records  unfortunately  do  not  give  informa- 

1Beitrage  zur  Statistick  der  Blitzschlage  in  Deutschland;  von  Dr.  Hellman,  Berlin, 
1886. 


9 


tion  as  to  the  extent  of  damage  to  property.  To  get  at  something 
like  a  fair  commercial  estimate  of  the  destruction  of  property  by 
lightning,  I  have  made  use  of  the  "  Chronicle  Fire  Tables  "  for  the 
eight  years  1885-'92.  It  is  hardly  necessary  to  remark  that  these 
tables  are  compiled  from  the  reports  of  the  fire  departments,  insurance 
companies,  and  the  reports  of  fires  in  the  public  press,  and  represent 
a  high  degree  of  accuracy. 

From  information  contained  in  these  volumes,  the  following  tables 
have  been  compiled : 

Fires  caused  by  lightning. 


Year. 

Number  of 
fires. 

LOBS  on  original 
risk. 

1885  to  1890,  inclusive  

2,  22O 

$8  386  826 

jgqi 

8V) 

Or,  in  eight  years,  ending  1892,  in  the  United  States,  and  for  the 
most  part  east  of  the  Rocky  Mountains,  3,516  fires,  with  a  loss  of 
$12,663,835. 

It  is  very  evident,  therefore,  that  the  damage  done  by  lightning  is 
no  inconsiderable  matter  to  be  lightly  passed  over  or  turned  off  by 
replies  such  as  the  one  given  by  the  Glasgow  manufacturers.  It  is 
certainly  worth  while  to  erect  the  proper  protective  apparatus. 

The  following  table  shows  the  number  of  barns,  stables,  granaries, 
churches,  and  dwellings  set  on  fire  by  lightning  during  the  years  1890, 
1891,  and  1892: 


Year. 

Barns, 
stables,  and 
granaries. 

Churches. 

Dwellings. 

jggo  

161 

29 

121 

1891        

ii 

78 

l8Q2 

During  nine  years  ending  1892,  2,335  barns,  104  churches,  and  664 
dwellings  have  been  struck  by  lightning. 

The  question  has  often  been  raised  whether  there  exists  a  periodicity 
in  the  number  of  lightning  strokes.  Statistics  must  cover  a  period 
of  at  least  twenty  years  before  an  answer  to  this  question  can  be  given, 
but  it  is  interesting  to  compare  the  number  and  kind  of  buildings 
struck  for  the  last  two  years  of  which  we  have  record. 


1891. 

I892. 

Barns,  granaries  and  stables      

290 
ii 

7! 

i 

2 
I 
IO 

495 

2§ 

177 

2 

4 

Churches                                                                                              .            

Dwell  ings  and  tenements                  .          

Grain  elevators         .        ..           

Grain  fields                                                                      

12 

10 


1891* 

1892. 

4 

4 

4 

4 

2 

i 

2 

2 

2 

22 

5 

7 

2 

3 

It  is  of  particular  interest  to  study  the  geographical  distribution  of 
the  dwellings  and  barns  struck  in  these  two  years.  There  are  some 
notable  increases  in  certain  States,  the  reasons  for  which  are  not  at 
present  discernable.  Attention  is  directed  to  the  figures  in  bold-face 
type. 


State. 

Barns. 

Dwellings. 

1891. 

1892. 

1891. 

1892. 

9 
4 
i7 
3i 
19 
i 
3 

21 
12 
12 
26 
7 
I 
2 
I 
2 
2 
H 
30 
26 

23 

I 

2 

4 

1 

:0 

5 

6 

16 

7 
7 

12 
9 

7 

16 

12 
13 
6 

8 

4 

i 

2 

3 

Nebraska                                                                  

North  Carolina                                                                                        •• 

3 

2 

30 
117 
26 

2 

3 

2! 

4 

New  York                                                  

Ohio  

29 
I 

3 
3 
4 

73 

4 

3 

23 

2 

Rhode  Island 

South  Dakota                                                                                       .  ... 

3 
7 

2 

3 

6 

11 

2 

According  to  the  statistics  of  the  German  bureau,  previously  re- 
ferred to,  the  frequency  of  lightning  stroke  varies  somewhat  with  the 
character  of  the  land.  Thus,  in  their  investigations  it  was  found  that 
in  flat  lands  400  to  540  buildings  were  struck  out  of  1,000,000,  the 
rate  varying  in  different  localities. 

The  nature  of  the  material  used  for  roofing  has  also  been  consid- 
ered. Classifying  the  various  materials  under  the  general  heads 
"  hard  "  and  "  soft,"  the  German  investigators  found  for  ten  years 
(1873-'83)  for  Schleswig-Holstein,  that  of  all  the  buildings  struck, 
9  per  cent  of  those  having  hard  roofs  and  68  per  cent  of  those  having 
soft  roofs  were  set  on  fire.  The  nature  of  the  building  and  the  pur- 
pose for  which  it  is  used  will,  as  we  readily  see  also  in  our  own  statis- 
tics, influence  the  liability  to  stroke  and  fire. 


11 

One  interesting  point  which  appears  to  be  shown  by  statistical 
studies  of  lightning  stroke  is  the  decreased  liability  to  accident  in 
thickly  settled  communities. 

It  may  be  said,  in  general,  that  the  risk  in  the  country  is  five 
times  greater  than  in  the  city.  For  ordinary  dwelling  houses,  not 
unduly  exposed  in  city  blocks,  lightning  rods  are  hardly  necessary, 
a  very  considerable  protection  being  afforded  by  the  tin  roofing, 
numerous  cornices,  gutters,  etc.  The  geological,  as  well  as  the  topo- 
graphical conditions,  may  have  some  influence  upon  the  frequency 
of  lightning  stroke.  According  to  the  authority  already  quoted,  if  1 
represents  the  frequency  of  lightning  stroke  in  a  chalk  formation,  2 
will  represent  the  liability  for  marl,  7  for  clay,  9  for  sand,  and  22 
for  loam. 

With  regard  to  trees,  the  oak  is  most  frequently,  and  the  beech 
least  frequently,  struck.  The  values  are  something  like,  if  1  repre- 
sents the  frequency  for  the  beech  tree,  15  for  pines,  other  trees  gen- 
erally averaged  at  40,  and  54  for  oaks.  Trees  struck  are  most  gen- 
erally those  standing  in  the  clear  or  on  the  edge  of  forests,  and  in 
height  averaging  from  16  to  20  meters  (52  to  66  feet).  The  trunk 
appears  to  be  struck  about  three  times  as  often  as  the  boughs,  and 
generally  the  stroke  seems  to  travel  to  the  ground.  Only  in  three 
out  of  a  hundred  cases  did  it  jump  to  other  trees. 

Mr.  Symons, 1  in  his  paper  on  thunderstorms,  instances  16  trees 
struck.  About  one-third  of  these  were  elms,  with  the  oak,  ash,  pop- 
lar, in  order  following,  and  one  case  each  of  crab-lime  and  willow. 

It  is  interesting  to  recall  at  this  point,  the  record  made  by  Hugh 
Maxwell  as  early  as  1787,  that  the  elm,  chestnut,  oak,  and  pine 
were  often  struck,  the  ash  rarely,  and  the  beech,  birch,  and  maple 
never.  This  last,  however,  is  not  true.  Indeed,  it  is  not  altogether 
plain  just  why  some  trees  escape  while  others  suffer.  Capt.  Maclear,3 
discussing  the  action  of  lightning  during  a  thunderstorm  on  June 
6  and  7,  1889,  found  a  great  number  of  trees  struck  within  a  jadius 
of  4  miles,  and  set  to  work  to  discover  if  possible  the  cause  of  the 
selection  of  these  particular  trees.  "  For  contrary  to  general  %ex- 
pectations,"  he  says,  "  they  were  not  the  highest  nor  the  most  prom- 
inent in  their  immediate  vicinity."  A  cottage,  a  haystack,  2  poplars, 
a  spruce,  fir,  and  5  oaks,  in  different  places,  were  struck  within  this 
confined  area. 

The  storm  passed  in  a  northwest  direction  with  southeast  wind,  and 
it  is  apparent  that  the  objects  struck  lie  nearly  in  a  line  northwest 
and  southeast,  3  miles  in  length.  "  The  spruce  was  very  prominent 
on  the  southern  brow  of  the  hill,  with  two  arms  nearly  in  line 
with  the  stem ;  one  arm  was  thrown  to  the  ground  and  the  other 

1  Also,  Appendix  E.     "  Report  of  Lightning  Rod  Conference." 
'"Quart.  Journ.  Met.  Soc."  1890,  p.  229. 


12 

blown  down.  At  the  juncture  of  the  arms  there  was  a  great  deal  of 
turpentine  which  was  thoroughly  blackened."  Hence,  it  is  assumed 
that  the  prominence  of  the  tree  made  it  the  best  communication  to 
earth,  and  that  the  collection  of  turpentine  was  raised  to  explosive 
temperature  and  split  the  tree,  but  a  like  good  reason  does  not  appear 
for  the  other  objects  struck.  On  the  next  day  6  oaks,  a  chestnut, 
and  an  ash,  in  various  positions  within  one-half  mile  of  a  pond,  and 
on  the  slope  of  ground  near  the  pond,  a  young  fir,  and  three  young 
oaks;  one-half  mile  south  of  Cranleigh  4  oaks;  'on  Cranleigh 
Common  an  oak,  and  1  mile  northwest  a  chimney,  a  stable,  and  an 
oak  (struck  also  on  the  day  before)  and  a  single  oak  occupying  a  fairly 
prominent  position  on  the  slope  of  high  hills,  2£  miles  northeast. 

This  last  tree  was  struck  just  before  the  rain  commenced  and  was 
split;  the  other  trees  struck  during  the  rain  were  only  scored. 
"Hence,"  concludes  Maclear,  "it  is  not  easy  to  see  the  cause  of  selec- 
tion, for  these  trees  were  not  the  most  prominent,  nor  were  they  on  the 
highest  ground  in  the  vicinity,  the  only  feature  the  groups  possessed  in 
common  being  that  they  were  all  either  near  ditches  which  were  full  of  run- 
ning water,  or  else  near  temporary  courses  taken  by  the  deluge  of  water  from 
the  higher  to  the  lower  ground.1  The  most  puzzling  case  is  that  of  the 
young  fir  tree  and  3  young  oaks  in  the  middle  of  the  copse  near  the 
pond.  They  were  not  higher  than  the  other  trees  on  the  copse,  but 
there  certainly  was  a  temporary  water  course  close  to  them ;  other 
trees,  however,  stood  equally  close  to  water.  *  *  *  Another  curious 
case  is  that  of  the  stable  struck,  which  was  overshadowed  by  tall 
elms,  where  it  might  have  been  supposed  that  these  would  have  taken 
the  stroke." 

Some  statistics  of  the  damage  done  by  lightning  stroke  in  Belgium2 
in  1889  may  be  appropriately  inserted  here.  Of  324  lightning  flashes, 
2  struck  lightning  rods;  123  struck  buildings,  setting  36  on  fire; 
16  struck  persons;  96,  trees;  81,  telegraph  and  telephone  lines; 
and  others,  miscellaneous.  In  other  statistics  we  find  that  of  18  deaths 
due  to  lightning;  1  occurred  within  a  dwelling,  11  out  of  doors,  and 
6  under  trees.  Contrasted  with  the  cases  of  death  resulting  from 
lightning  stroke,  let  us  look  at  43  cases  of  persons  struck,  with  results 
not  necessarily  fatal,  and  we  find  that  20  of  these  were  in  doors,  23 
out  of  doors,  including  4  under  trees.  No  records  sufficiently  extended 
and  authentic  are  available  to  ascertain  what  proportion  of  persons 
struck  by  lightning  are  killed  outright.  I  know  of  but  one  record, 
and  in  that  of  212  persons  struck  74  were  killed.  This  question,  which 
is  of  the  greatest  interest,  is  referred  to  again  under  the  last  of  the 
rules  given  further  on  for  the  protection  of  life. 

One  of  the  peculiar  and  most  common  characteristics  of  the  action 

1  Italics  mine. 

»Evrard  and  Lambotte.     del  et  Tcrrc,  1891;  No.  7. 


13 

of  lightning  is  the  tearing  off  or  throwing  effect.  This,  as  we  shall 
see  further  on,  is  just  what  might  be  expected  from  discharges  of 
great  frequency  of  alternation.  Some  interesting  statistics  are  given 
by  Parnell l  on  the  mechanical  tearing  off  and  disruptive  effects  of 
lightning  as  distinguished  even  from  the  heat  effects.  He  records 
1,147  cases.  Of  these,  224  do  not  permit  a  determination  of  the 
character  of  the  work  done  by  the  stroke  of  the  remaining  923. 


Mechanical 
work. 

Heat. 

52 
88 

<£ 

206 

1 

60 

79 
79 

2 

1 

Masonry  01  all  kinds  

Glass  china  earthenware                             .                    

Metal    .                               

Wood  

Trees    

Thatch  straw,  etc         

II 
15 
19 

1,221 

485 

Col.  Parnell  gives,  furthermore,  the  details  in  278  cases  to  show  the 
existence  of  an  upward  direction  in  the  force  of  the  stroke. 

This,  and  the  statement  that  "  probably  few  persons  are  aware  that 
lightning  strokes  are  more  apt  to  bend  or  break  metal  than  to  fuse 
it,"  are,  in  the  light  of  the  investigations  of  the  past  three  years  into 
the  character  of  the  lightning  flash,  easily  comprehensible.  A  light- 
ning flash  being  a  break  in  the  air  (i.  e.,  the  dielectric)  when  the 
electrical  strain  exceeds  a  certain  value,  determined  by  several  vari- 
ables, the  strongest  mechanical  effect  may  be  found  in  any  direction, 
upward  or  downward.  Speaking  popularly,  flashes  may  go  from 
cloud  to  earth,  earth  to  cloud,  or  from  cloud  to  cloud  to  earth. 

n. 

Beyond  doubt,  Franklin  proved  his  case  that  lightning  rods  were 
efficacious  in  the  protection  of  buildings.  An  illustration  of  the 
action  of  lightning  upon  a  rod  is  shown  in  Fig.  4.  Buildings  with 
conductors  when  struck  by  lightning  suffered  little  damage  compared 
with  those  without  protectors. 

The  chief  defects  likely  to  occur  are  blunted  points  and  breaks  in 
the  continuity  of  the  connection.  The  function  of  a  lightning  rod  is 
twofold ;  first,  that  of  conducting  the  charge  to  earth,  and  second, 
the  prevention  of  a  disruptive  discharge  by  silent  neutralization  of 
the  cloud  electrification.  The  latter  explains  why  a  rod  terminates 
in  a  point  and  likewise  why  points  in  good  connection  with  the  ground 
are  always  desirable  upon  buildings.  Indeed,  points  are  somewhat 
like  small  water  pipes  connected  with  a  large  reservoir.  If  you  have 

1 "  Quart.  Journ.  Met  Soc.,"  Vol.  vi,  1886.      See  also  Col.  ParneU's  book. 


14 

enough  of  them  and  a  sufficient  time  you  may  drain  the  largest  reser- 
voir. Furthermore,  when  some  sudden  rise  or  flood  occurs  in  the 
reservoir,  these  minute  drains  may  be  of  service  in  keeping  the  height 
of  the  water  down. 

In  the  case  of  lightning  the  points  are  the  small  escape  pipes,  the 
layer  of  air  between  cloud  and  earth  the  retaining  wall,  and  the 
cloud  electrification — or  charge — the  overflowing  and  destructive  ele- 
ment. A  large  conductor,  be  it  rod  or  tape,  on  the  other  hand  is 
more  like  a  large  main  or  water  way,  which  has  its  gate  shut  until 
the  flood  is  imminent.  Then  the  gate  is  suddenly  opened  and  we  try 
to  compel  the  torrent  to  keep  to  the  provided  path.  We  trust  in  its 
ability  to  safely  hold  the  flood.  Generally  it  does.  In  perhaps  nine 
cases  out  of  ten,  the  lightning  conductor,  if  it  be  such  a  one  as  we 
will  describe  later,  does  carry  the  flash  to  earth ;  but  there  are  cases 
where  the  discharges  have  been  heavy  and  overflows  have  resulted. 
To  carry  the  lightning  flash  "  the  lightning  conductor  should  offer  a 
line  of  discharge  more  nearly  perfect  and  more  accessible  than  any 
other  offered  by  the  materials  or  contents  of  the  edifice  we  wish  to  pro- 
tect." To  prevent  the  discharge  "  the  conductor  should  be  surrounded 
by  points."  These  quotations  are  from  the  Report  of  the  Lightning 
Rod  Conference. 

The  statement  that  lightning  always  follows  the  path  of  least  resis- 
tance, as  commonly  understood  and  stated,  needs  modification.  True 
it  is,  that  when  the  air  is  strained  by  being  subjected  to  the  electrifi- 
cations of  cloud  and  earth,  the  weakest  spot  gives  away  first,  and  this 
is  apt  to  be  in  line  with  some  small  elevated  knob  or  surface ;  but  it 
is  equally  true,  and  is  perhaps  the  more  general  case,  that  when  a 
really  vigorous  disruptive  discharge  does  occur,  it  is  somewhat,  as 
Dr.  Lodge  aptly  puts  it,  like  an  "  avalanche."  As  a  matter  of  fact, 
we  find  from  the  study  of  actual  cases  where  buildings  have  been 
struck,  that  lightning  often  disregards  entirely  metallic  surfaces' 
and  points.  What  we  should  first  know  is,  whether  the  condition 
is  to  be  one  of  "  steady  strain  " l  or  "  impulsive  rush  "  l  discharge. 
In  the  case  of  "  steady  strain,"  the  metal  is  apt  to  influence  the  path 
of  discharge ;  in  the  case  of  an  "  impulsive  rush "  discharge,  even 
points  seem  to  lose  their  efficiency  and  become  of  little  use. 

In  a  letter 2  of  an  old  British  admiral  there  occurs  a  description  of 
his  being  called  upon  to  approve  some  specifications  for  a  lightning 
conductor  to  be  erected  on  a  certain  lighthouse.  He  was  himself  a 
believer  in  the  "surface"  theory  of  Harris;  but  thought  that,  to 
make  sure,  he  would  go  and  consult  his  friend  Faraday.  Faraday, 
who  saw  only  the  question  of  conductivity  in  the  problem,  said  very 
positively  that  the  solid  rod  was  better  than  the  tube  (which  gives 

1  Terms  used  by  Prof.  Lodge. 

1  See  report  of  Lightning  Rod  Conference. 


15 

greater  surface  with  less  copper),  and  that  solid  volume  was  everything, 
superficial  area  nothing.  Moreover,  if  Harris  says  otherwise  "  then, 
he  knows  nothing  whatever  about  it."  The  admiral  straightway  ap- 
proved the  solid  rod  conductor  for  the  lighthouse.  Within  two  or 
three  days  he  met  Harris,  and  bringing  up  the  question  was  told  by 
Harris  "  surface  area  is  most  important,  and  if  Faraday  says  other- 
wise, then  he  knows  nothing  whatever  about  it!" 

Up  to  a  certain  point  Faraday  was  right ;  a  copper  rod  an  inch 
thick  is  capable  of  carrying  almost  any  flash  of  lightning,  and  is  un- 
doubtedly a  great  protector,  but  if,  as  we  have  reason  to  believe,  the 
core  is  seldom  given  a  chance  to  carry  the  current,  why  have  it  ?  The 
views  of  Sir  W.  Snow  Harris,  based  as  they  were  upon  close  study  of 
many  thousand  cases  of  lightning  action,  are  finding  in  the  experi- 
ments of  to-day  the  confirmation  so  long  needed. 

While  not  going  into  details  regarding  this  question  of  the  shape 
of  the  rod,  let  us  emphasize  the  fact,  so  recently  brought  out,  that  if 
an  electric  current  flows  steadily  in  one  direction  in  a  cylindrical 
wire,  its  intensity  is  the  same  in  all  portions  of  the  wire,  as  shown 
by  Hertz,  but  that  with  a  current  of  an  oscillatory  character,  i.  e.,  a 
current  which  rapidly  reverses  its  direction,  this  condition  no  longer 
holds,  and  if  the  direction  is  altered  very  rapidly  the  interior  of  the 
wire,  in  our  case  the  lightning  rod,  may  be  almost  free  from  current. 

In  1882  appeared  the  report  of  the  Lightning  Rod  Conference ;  in 
many  respects  the  most  important  contribution  to  the  literature  of 
the  subject  yet  made.  While  so  many  foreign  governments,  and  in 
particular  France,  had  by  means  o'f  officially  constituted  boards 
taken  a  governmental  interest  in  the  protection  of  the  people  from 
the  dangers  of  lightning,  the  English-speaking  people  of  the  world 
aside  from  the  few  directions  officially  issued  for  the  protection  of 
magazines  and  lighthouses,  remained  without  any  authoritative  utter- 
ance upon  the  subject;  and  while  this  conference  itself  did  not  have 
strictly  official  sanction,  it  carries,  from  the  character  of  its  make- 
up, a  weight  certainly  as  great,  if  not  greater,  than  an  official  board. 
It  was  simply  a  joint  committee  of  representative  members  of  the 
Institute  of  British  Architects,  the  Physical  Society,  the  Society  of 
Telegraph  Engineers  and  Electricians,  the  Meteorological  Society, 
and  two  co-opted  members.  As  might  be  anticipated  from  such  aus- 
pices, the  report  is  an  excellent  one,  and  must  stand  forbears  as  the 
embodiment  of  the  most  widely  gathered  information  and  well-con- 
sidered decisions.  The  report  is  emphatically  one  based  upon  expe- 
rience. 

The  famous  free-for-all  discussion  which  occurred  at  the  British 
Association  Meeting  in  1888,  so  far  as  our  judgment  goes,  simply 
proved  that  the  decisions  of  the  conference  could  not  at  present  be 
disregarded.  As  the  president  of  the  meeting,  Sir  William  Thomson 


16 

said,  we  have  "  very  strong  reason  to  feel  that  there  is  a  very  com- 
fortable degree  of  security,  if  not  of  absolute  safety,  given  to  us  by 
lightning  conductors  made  according  to  the  present  and  orthodox 
rules." 

There  are  one  or  two  further  features  to  which  attention  may  be 
called.  There  are  some  very  prevalent  misapprehensions  with  regard 
to  lightning.  For  example :  that  it  never  strikes  twice  in  the  same 
place;  that  the  most  exposed  place  is  always  struck;  that  a  few 
inches  of  glass  or  a  few  feet  of  air  will  serve  as  a  competent  insulator 
to  bar  the  progress  of  a  flash  that  has  forced  its  way  through  a  thou- 
sand feet  of  air,  etc.  These  are  alluded  to  in  the  following  general 
directions. 

in. 

1.  Erection  of  rods.     Few  questions  have  been  so  thoroughly  dis- 
cussed from  practical  as  well  as  theoretical  standpoints  as  that  of  the 
certainty  of  the  protection  afforded  by  properly  constructed  lightning 
rods.     All  barns  and  exposed  buildings  should  have  lightning  rods. 
Ordinary  dwelling  houses  in  city  blocks  have  not  the  need  for  rods 
that  scattered  houses  in  the  country,  and  especially  if  on  hill  sides, 
have. 

2.  Use  a  good  iron  or  copper  conductor.     If  the  latter,  one  weigh- 
ing about  6  ounces  to  the  foot,  and  preferably  in  the  form  of  tape. 
If  iron  is  used  and  it  seems  to  be  in  every  way  as  efficient  as  copper, 
have  it  in  rod  or  tape  form  and  weighing  about  35  ounces  to  the  foot. 
"A  sheet  of  copper  constitutes  a  conductive  path  for  the  discharge 
from  a  lightning  stroke  much  less  impeded  by  self-induction  than 
the  same  quantity  of  copper  in  a  more  condensed  form,  whether  tab- 
ular or  solid."     (Sir  William  Thomson.) 

3.  The  nature  of  the  locality  (see  Chapter  I)  will  determine  to  a 
great  degree  the  need  of  a  rod.     Places  apart  but  a  few  miles  will 
differ  greatly  in  the  relative  frequency  of  flashes.     In  some  localities 
the  erection  of  a  rod  is  imperative ;  in  others,  hardly  necessary. 

4.  The  very  best  ground  you  can  get  is,  after  all,  for  some  flashes 
but  a  very  poor  one ;  therefore,  do  not  imagine  that  you  can  overdo 
the  matter  in  the  making  of  a  good  ground.     For  a  great  many  flashes 
an  ordinary  ground  suffices,  but  the  small  resistance  of  ^  ohm  for 
an  intense  oscillatory  flash  may  be  dangerous.     B  ary  the  earth  plates 
in  damp  earth  or  running  water. 

5.  "If  the  conductor  at  any  part  of  the  course  goes  near  water  or 
gas  mains,  it  is  best  to  connect  it  to  them.     Wherever  one  metal  ram- 
ification approaches  another  it  is  best  to  connect  them  metallically. 
The  neighborhood  of  small  bore  fusible  gas  pipes  and  indoor  gas  pipes 
in  general  should  be  avoided."     (Lodge.) 


17 

6.  The  top  of  the  rod  should  be  plated  or  in  some  way  protected 
from  corrosion  and  rust. 

7.  Independent  grounds  are  preferable  to  water  and  gas  mains. 

8.  Clusters  of  points  or  groups  of  two  or  three  along  the  ridge  rod 
are  recommended. 

9.  Chain  or  linked  conductors  are  of  little  use. 

10.  Area  of  protection.     Very  little  faith  is  to  be  placed  in  the  so- 
called  area  of  protection.     The  committee  that  first  gave  authority  to 
this  belief  considered  that  the  area  protected  by  any  one  rod  was  one 
with  a  radius  equal  to  twice  the  height  of  the  conductor  from  the 
ground.     Many  lightning  rod  manufacturers  consider  that  the  rod 
protects  an  area  of  radius  equal  to  the  height.     The  truth  is  that 
buildings  are  struck  sometimes  within  this  very  area,  and  we  now 
hold  there  is  no  such  thing  as  a  definite  protected  area. 

11.  Return  shock.     Some  uncertainty  exists  on  this  point.     The  so- 
called  "return   stroke"  is  caused  by  the   inductive   action  of  the 
charged  cloud  on  bodies  within  its  influence,  and  yet  some  distance 
away  from  the  place  of  the  direct  discharge.     As  explained  by  Lord 
Mahon,  who  first  called  attention  thereto,  the  sudden  return  of  the 
body  charged  inductively  to  a  neutral  condition,  following  the  equal- 
ization at  some  distant  place,  is  the  cause  of  the  return  shock.     We 
are  beginning,  however,  to  see  more  clearly  into  the  character  of  the 
stress  in  the  dielectric,  preceding  and  during  flashes,  and  it  is  only  a 
question  of  time  before  the  use  of  this  term,  "  return  shock,"  will  be 
abandoned.     Of  far  greater  import  are  the  terms  "  recoil  kick  "  and 
"  alternative  path,"  as  shown  experimentally  by  Lodge  to  exist. 

12.  Upward  motion  of  stroke.     There  is  no  reason  to  doubt  that  the 
discharge  takes  place  sometimes  from  earth  to  cloud.     That  is  to  say, 
that  while  we  now  consider  a  lightning  flash  as  something  like  the 
discharge  of  a  condenser  through  its  own  dielectric,  made  up  of  exces- 
sively frequent  alternations,  say  something   like  300,000  times  per 
second,  the  spark,  or  core   of  incandescent  air,  may  seem  to  have 
had  its  beginning  at  the  earth's  surface.     That  is  to  say,  the  air  gap 
breaks  down  first  at  a  point  near  the  earth. 

13.  Indifference  of  lightning  to  the  path  of  least  resistance.    Nearly 
all  treatises  upon  lightning  up  to  within  very  recent  times,  assumed 
that  lightning  always  followed  the  path  of  least  resistance.     "  It  is 
simply  hopeless  to  pretend  to  be  able,"  says  Lodge,  "  to  make  the 
lightning  conductor  so  much  the  easier  path  that  all  others  are  out 
of  the  question."     The  path  will  depend  largely  upon  the  character 
of  the  flash. 

14.  Any  part  of  a  building,  if  the  flash  be  of  a  certain  character, 
may  be  struck,  whether  there  is  a  rod  on  the  building  or  not.    Fortu- 
nately, these  are  exceptional  instances.     The  great  majority  of  flashes 
in  our  latitudes  are  not  so  intense  but  that  a  good  lightning  rod,  well 


18 

earthed,  makes  the  most  natural  path  for  the  flash.  We  have  many 
instances,  however  (not  to  be  confounded  with  cases  of  defective 
rods),  where  edifices,  seemingly  well  protected,  have  been  struck 
below  the  rods. 

15.  Parodox  of  parodoxes,  a  building  may  be  seriously  damaged  by 
lightning  without  having  been  struck  at  all.     Take  the  famous  Hotel 
de  Ville  of  Brussels.     This  building  was  so  well  protected  that  scien- 
tific men  pronounced  it  the  best  protected  building  in  the  world  against 
lightning.     Yet  it  was  damaged  by  fire  caused  by  a  small  induced 
spark  near  escaping  gas.     During  the  thunderstorm,  some  one  flash 
started  "  surgings  "  in  a  piece  of  metal  not  connected  in  any  way 
with  the  protective  train  of  metal.     The  building  probably  did  not 
receive  even  a  side  flash.     This  is,  therefore,  a  new  source  of  danger 
from  within,  and  but  emphasizes  the  necessity  of  connecting  metal 
with  the  rod  system. 

16.  Lightning  does   sometimes    strike   twice   in   the   same   place. 
Whoever  studies  the  effects  of  lightning's  action,  especially  severe 
cases,  is  almost  tempted  to  remark  that  there  is  often  but  little 
left  for  the  lightning  to  strike  again.     No  good  reason  is  known  why 
a  place  that  has  once  been  struck  may  not  be  struck  again.     There 
are  many  cases  on  record  supporting  the  assertion. 

17.  As  lightning  often  falls  indiscriminately  upon  tree,  rock,  or 
building,  it  will  make  but  little  difference  sometimes  whether  trees 
are  higher  than  adjoining  buildings. 

18.  It  is  not  judicious  to  stand  under  trees  during  thunderstorms, 
in  the  doorway  of  barns,  close  to  cattle,  or  near  chimneys  and  fire 
places.     On  the  other  hand,  there  is  not  much  sense  in  going  to  bed 
or  trying  to  insulate  one's  self  in  feather  beds.     Small  articles  of 
steel,  also,  do  not  have  the  power  to  attract  lightning,  as  it  is  popu- 
larly put,  or  determine  the  path  of  discharge. 

19.  Unnecessary  alarm.    Just  in  advance  of  thunderstorms,  whether 
because  of  the  varying  electrical  potential  of  the  air,  or  of  the  changing 
conditions  of  temperature,  humidity,  and  pressure,  and  failure  of  the 
nervous  organization  to  respond  quickly,  or  to  whatever  cause  it  may 
be  due,  it  cannot  be  denied  that  there  is  much  suffering  from  depres- 
sion, etc.,  at  these  times.     It  is,  perhaps,  possible  that  these  suffer- 
ings may  be  alleviated.     Apart  from  this,  many  people  suffer  greatly 
from  alarm  during  the  prevalence  of  thunderstorms,  somewhat  un- 
necessarily, we  think.     Grant  even  that  the  lightning  is  going  to 
strike  close  in  your  vicinity.     There  are  many  flashes  that  are  of  less 
intensity  than  we  imagine,  discharges  that  the  human  body  could 
withstand   without    permanent  serious   effects.      Voltaire's  caustic 
witticism  "  that  there  are  some  great  lords  which  it  does  not  do  to 
approach  too  closely,  and  lightning  is  one  of  these,"  needs  a  little 
revision  in  these  days  of  high  potential  oscillatory  currents.    Indeed, 


19 

the  other  saying,  "  Heaven  has  more  thunders  to  alarm  than  thunder- 
bolts to  punish,"  has  just  so  much  more  point  to  it,  as  it  is  nearer  the 
truth.  One  who  lives  to  see  the  lightning  flash  need  not  concern  him- 
self much  about  the  possibility  of  personal  injury  from  that  flash. 

20.  Finally,  if  you  should  be  in  the  vicinity  of  a  person  who  has 
just  been  struck  by  lightning,  no  matter  if  the  person  struck  appears 
to  be  dead,  go  to  work  at  once  and  try  to  restore  consciousness.  There 
are  many  cases  on  record  proving  the  wisdom  of  this  course ;  and 
there  is  reason  for  believing  that  lightning  often  brings  about  sus- 
pended animation  rather  than  somatic  death.  Try  to  stimulate  the 
respiration  and  circulation.  Do  not  cease  in  the  effort  to  restore  ani- 
mation in  less  than  one  hour's  time.  For  an  excellent  illustration 
of  a  case  of  severe  lightning  shock  and  recovery,  due,  it  would  seem, 
to  prompt  action  by  the  medical  gentlemen  present,  all  who  are  inter- 
ested may  consult  the  "Medical  News,"  August  11,  1888.  A  num- 
ber of  cases  corroborative  of  this  view  are  on  record  in  various  medi- 
cal journals. 

IV. 

A  practical  application  of  the  efficiency  of  lightning  conductors 
will  now  be  considered.  On  June  5, 1885,  the  Washington  Monument, 
at  Washington,  D.  C.,  at  that  time  the  highest  edifice  in  the  world, 
was  struck  by  lightning.  The  barograph  curve  (Fig.  6)  shows  the 
fluctuation  in  pressure  about  the  time  of  the  occurrence  of  the  stroke, 
3.15  p.  m.  The  storm  itself  was,  as  usual,  a  secondary  depression  in 
the  southeastern  or  southern  quadrant  of  a  "  low  "  area,  and  at  Wash- 
ington resulted  in  a  high  forenoon  temperature,  with  a  maximum  of 
90°  F.  about  noon,  with  fresh  southerly  winds,  veering  to  southwest 
at  noon;  to  northwest  at  1.23  p.  m.;  to  northeast  at  1.40  p.  m.,  and 
backing  to  northwest  at  1.42  p.  m. ;  to  east  at  2.20  p.  m. ;  to  north- 
west at  2.37  p.  m.,  and  veering  to  northeast  at  2.40  p.  m.,  from  whence  it 
shifted  to  southwest  at  3.02  p.  m. ;  to  northwest  at  3.10  p.  m.,  and  at 
7  p.  m.  was  blowing  steadily  from  the  north.  The  first  thunder  was 
heard  at  1.07  p.  m.,  and  rain  began  at  1.23  p.  m.,  ceasing  at  2  p.  m., 
commencing  again  at  2.20  p.  m.,  and  ending  at  3.05  p.  m.  Thunder 
continued  at  frequent  intervals  to  3.50  p.  m.  The  rain  was  at  times 
heavy,  and  hail  fell  in  the  northern  part  of  the  city.  Amount  of 
rainfall  at  Signal  Office,  0.61  inch. 

Col.  Casey,  U.  S.  Army,  the  engineer  in  charge  of  the  construction 
of  the  monument,  requested  Profs.  Rowland,  Newcomb,  and  Menden- 
hall  to  examine  the  part  struck  and  suggest  what  precautions  should 
be  taken  to  ensure  the  safety  of  the  monument.  It  is  proper  to  re- 
mark that  the  monument  had  been  for  all  practical  purposes  finished 
and  had  already  experienced  storms  of  seemingly  greater  violence. 


20 

From  the  letter l  of  the  commissioners  charged  with  the  completion 
of  the  monument,  we  find  that  "  a  considerable  amount  of  unexpected 
work  "  was  performed  in  the  erection  of  rods  and  points  to  protect 
the  obelisk  from  lightning.  "  The  lightning  protectors  as  established 
for  the  monument  were  commenced  in  January,  1880,  and  were  fin- 
ished in  January,  1885,"  practically  the  date  of  completion  of  the 
monument.  The  elevation  of  the  solid  aluminium  pyramid  (which 
weighs  100  ounces  and  is  8.9  inches  high  and  5.6  inches  square  at  base, 
with  angle  at  the  vertex  of  34°  48')  is  555  feet  (169.16  meters). 

The  conductors  consist  of  the  four  hollow  wrought-iron  Phoe- 
nix columns,  supporting  the  elevator  machinery.  "  The  bottoms  of 
these  four  columns  rest  upon  and  are  bolted  to  cast-iron  shoes,  stand- 
ing upon  the  floor  of  the  large  drum  pit,  *  *  *  and  the  shoes  are 
connected  to  f-inch  soft  copper  rods,  led  to  the  bottom  of  a  well  in 
the  center  of  the  foundation.  This  well  is  32  feet  10  inches  in  depth 
below  the  bottom  of  the  drum  pit  and  15  feet  8  inches  below  the  bot- 
tom of  the  masonry  foundation,  and  the  water  stands  in  it  per- 
manently 2  feet  8  inches  above  its  bottom.  After  the  copper  rods 
were  inserted  the  well  was  filled  up  with  clean  sharp  sand  for  a  depth 
of  15  feet  8  inches,  or  up  to  the  level  of  the  bottom  of  the  old  rubble- 
stone  foundation  of  the  monument.  These  four  columns  so  arranged 
at  their  bases,  and  always  projecting  above  the  top  of  the  shaft,  were  con- 
tinually lengthened  as  the  building  of  the  shaft  progressed,  and  for  the 
five  summers  during  which  the  masonry  was  in  progress  acted  as  the  light- 
ning conductors  of  the  edifice.3  No  disruptive  discharge  of  electricity 
was  experienced  during  those  years."  When  the  marble  pyramidion 
was  completed,  December,  1884,  these  four  columns  were  within  this 
marble  covering,  and  from  the  extremity  of  each  column  a  copper 
rod  J  inch  in  diameter  was  run  to  the  top  stone  and  there  united  in 
a  copper  rod  1^  inches  in  thickness,  which  passed  vertically  through 
the  cap  stone  and  was  screwed  into  the  solid  aluminium  pyramid. 

The  conductors  "when  tested,  gave  an  electrical  resistance  of  .1 
ohm  from  the  tip  of  the  terminal  to  the  copper  rods  at  the  base,  and 
2.2  ohms  for  the  ground  connections,  making  a  total  resistance  of  2.3 
ohms  for  the  conductor.  The  system  was  entirely  completed  and 
connected  on  January  20,  1885." 

On  April  5,  1885,  during  the  passage  of  a  heavy  thundercloud  over 
the  monument,  at  least  five  immense  sparks  or  bolts  of  electrical 
light  were  seen  within  a  period  of  twenty  minutes  to  flash  between 
the  terminals  and  the  cloud  without  audible  sound  to  the  observers. 
A  careful  examination  of  the  conductors  and  shaft  after  this  phe- 
nomena failed  to  reveal  any  effects  from  these  discharges. 

On  June  5,  however,  during  the  thunderstorm  described  above,  a 

1  Senate  Ex.  Doc.  No.  6,  49th  Congress,  1st  session. 
'Italics  mine. 


21 

disruptive  discharge  was  seen  to  pass  between  the  summit  of  the 
pyramidion  and  the  cloud.  Upon  examining  the  structure  a  crack 
was  discovered  in  the  stone  on  the  north  face  of  the  pyramidion  just 
under  the  top  stone,  extending  through  the  block  in  a  line  nearly 
parallel  to  the  northeast  corner  and  about  8-J-  inches  from  it.  ( Fig. 
5.)  The  fragment  was  pressed  outward  about  }  inch  at  its  bottom, 
chipping  a  small  piece  off  the  lower  corner  of  the  top  stone  into 
which  it  was  locked,  and  was  easily  forced  back  to  place  and  bolted 
to  the  solid  stone  from  which  it  had  been  torn. 

The  recommendations  of  the  gentlemen  above  named,  who  were 
asked  to  make  a  careful  examination,  were,  in  short,  that  the  interior 
conductors  should  be  connected  "with  a  system  of  rods  and  a  greater 
number  of  points,  to  be  located  upon  the  exterior  of  the  pyramidion." 
Four  |-inch  copper  rods  were  fastened  by  a  band  to  the  aluminium 
terminal  and  led  down  the  corners  to  the  base  of  the  pyramidion, 
and  then  through  the  masonry  to  the  columns. 

"As  these  exterior  rods  are  each  over  60  feet  long,  they  are  also 
connected  at  two  intermediate  points  of  their  lengths  with  the  iron 
columns  by  means  of  copper  rods  -J  and  j  inch  in  diameter,  respect- 
ively, furnishing  16  rods  in  all,  connecting  the  exterior  system  of 
conductors  with  the  interior  conducting  columns.  Where  the  exte- 
rior rods  upon  the  corners  cross  the  11  highest  horizontal  joints  of 
the  masonry  of  the  pyramidion  they  are  connected  to  each  other  all 
around  by  other  copper  rods  sunk  into  those  joints.  All  of  these 
exterior  rods,  couplings,  and  fittings  are  gold  plated,  and  are  studded 
at  every  5  feet  of  their  lengths  with  copper  points  3  inches  in  length, 
gold  plated  and  tipped  with  platinum.  There  are  200  of  these  points 
in  all." 

Eight  years  have  now  passed  since  the  alterations  were  made  and 
the  monument  stands  uninjured.  Unquestionably,  standing  as  it 
does,  555  feet  high,  in  the  center  of  flat,  well-watered  ground,  it  con- 
stitutes a  'most  dangerous  exposure  for  lightning  flashes.  No  better 
illustration  of  the  value  of  lightning  conductors  can  be  asked. 


Fig.  1.  Conductors  and  fastenings.     From  Anderson,  and  Lightning  Rod  Conference 

Report. 


Fig.  2.  Chimney,  struck  July  29,  1890.     From  Eke.  Zeits.,  Grebel. 


Fig.  3.  Washington  Monument,  struck  June  5,  1885. 


Q/umimam  r,p  neighing  /OOo*,. 
arly  9  "high  5 k"  square  <ar  bas&, 
tfeigM  from  ground  555  Fr  (/f>9mef res) 


-     June  5T? 

face  jusr  under  rop  &rone.  e 
irr£  fhrouGh  ffre  b/nck  in<a  //n& 
near/y  parallel  to  NE  corner. 

Fig.  4.  Rod  melted  by  lightning.       Fig.  5.  Aluminium  tip  of  Washington  Monument. 
From  Franklin's  Works. 


29.60 


Curw  of    t/Itntospherio  JPressitre 


WixsMn.0ton.l>.C. 


iZ  M  JKM  2 


Fig.  Q.  Curve  of  barometric  pressure. 


I 


00 

fcJO 


I 

a 


14  DAY  USE 

RETURN  TO  DESK  EROM  WHICH  BOKROWE, 

LOAN  DEPT. 


LD  2lA-40ro-ll,'63 
(E1602slO)476B 


General  Library 
UnivSityofCalifortua 

Berkeley 


YB  5196 


